rs187379039

chr15-90763056-T-C

Variant summary

Our verdict is Uncertain significance. Variant got 0 ACMG points: 2P and 2B. PM2 BP4_Moderate

The NM_000057.4(BLM):c.1973T>C(p.Ile658Thr) variant causes a missense change. The variant allele was found at a frequency of 0.0000112 in 1,614,034 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a benign outcome for this variant. Variant has been reported in ClinVar as Uncertain significance (★★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. I658V) has been classified as Uncertain significance.

• Frequency:
  • Genomes: 𝑓 0.0000066 (0 hom., cov: 32)
  • Exomes 𝑓: 0.000012 (0 hom.)
• Consequence: BLM NM_000057.4 missense
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:2
• Conservation: PhyloP100: 6.19

Genes affected

BLM (HGNC:1058): (BLM RecQ like helicase) The Bloom syndrome is an autosomal recessive disorder characterized by growth deficiency, microcephaly and immunodeficiency among others. It is caused by homozygous or compound heterozygous mutation in the gene encoding DNA helicase RecQ protein on chromosome 15q26. This Bloom-associated helicase unwinds a variety of DNA substrates including Holliday junction, and is involved in several pathways contributing to the maintenance of genome stability. Identification of pathogenic Bloom variants is required for heterozygote testing in at-risk families. [provided by RefSeq, May 2020]

ACMG classification

Verdict is Uncertain_significance. Variant got 0 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• BP4: Computational evidence support a benign effect (MetaRNN=0.2375685).

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
BLM	NM_000057.4	c.1973T>C	p.Ile658Thr	missense_variant	8/22	ENST00000355112.8

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
BLM	ENST00000355112.8	c.1973T>C	p.Ile658Thr	missense_variant	8/22	1	NM_000057.4	P2

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD3 exomes AF: 0.00000398 AC: 1 AN: 251216 Hom.: 0 AF XY: 0.00 AC XY: 0 AN XY: 135782

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.0000289

Gnomad ASJ exome AF: 0.00

Gnomad EAS exome AF: 0.00

Gnomad SAS exome AF: 0.00

Gnomad FIN exome AF: 0.00

Gnomad NFE exome AF: 0.00

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.0000116 AC: 17 AN: 1461800 Hom.: 0 Cov.: 31 AF XY: 0.0000124 AC XY: 9 AN XY: 727206

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.00

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.0000252

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.0000135

Gnomad4 OTH exome AF: 0.0000166

GnomAD4 genome AF: 0.00000657 AC: 1 AN: 152234 Hom.: 0 Cov.: 32 AF XY: 0.00 AC XY: 0 AN XY: 74434

Gnomad4 AFR AF: 0.00

Gnomad4 AMR AF: 0.0000654

Gnomad4 ASJ AF: 0.00

Gnomad4 EAS AF: 0.00

Gnomad4 SAS AF: 0.00

Gnomad4 FIN AF: 0.00

Gnomad4 NFE AF: 0.00

Gnomad4 OTH AF: 0.00

ExAC AF: 0.00000824 AC: 1

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:2

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Bloom syndrome Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Invitae

Nov 04, 2023

This sequence change replaces isoleucine, which is neutral and non-polar, with threonine, which is neutral and polar, at codon 658 of the BLM protein (p.Ile658Thr). This variant is not present in population databases (gnomAD no frequency). This variant has not been reported in the literature in individuals affected with BLM-related conditions. ClinVar contains an entry for this variant (Variation ID: 579265). Advanced modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) performed at Invitae indicates that this missense variant is not expected to disrupt BLM protein function with a negative predictive value of 80%. Experimental studies have shown that this missense change does not substantially affect BLM function (PMID: 23129629). In summary, the available evidence is currently insufficient to determine the role of this variant in disease. Therefore, it has been classified as a Variant of Uncertain Significance. -

Hereditary cancer-predisposing syndrome Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Ambry Genetics

May 14, 2023

The p.I658T variant (also known as c.1973T>C), located in coding exon 7 of the BLM gene, results from a T to C substitution at nucleotide position 1973. The isoleucine at codon 658 is replaced by threonine, an amino acid with similar properties. One yeast-based functional assay showed that p.I658T behaves similarly to wild-type (Mirzaei H et al. Proc Natl Acad Sci U S A 2012 Nov;109(47):19357-62). This amino acid position is well conserved in available vertebrate species. In addition, the in silico prediction for this alteration is inconclusive. Since supporting evidence is limited at this time, the clinical significance of this alteration remains unclear. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Benign	0.31
BayesDel_addAF	Pathogenic	0.21	D
BayesDel_noAF	Uncertain	0.070
Cadd	Uncertain	23
Dann	Uncertain	1.0
DEOGEN2	Benign	0.40	T;.
Eigen	Benign	0.18
Eigen_PC	Uncertain	0.32
FATHMM_MKL	Pathogenic	0.99	D
LIST_S2	Uncertain	0.89	D;D
M_CAP	Benign	0.053	D
MetaRNN	Benign	0.24	T;T
MetaSVM	Benign	-0.39	T
MutationAssessor	Uncertain	2.4	M;.
MutationTaster	Benign	1.0	D;D
PrimateAI	Uncertain	0.70	T
PROVEAN	Uncertain	-4.2	D;D
REVEL	Uncertain	0.57
Sift	Uncertain	0.0060	D;T
Sift4G	Uncertain	0.0040	D;D
Polyphen		0.12	B;.
Vest4		0.44
MVP		0.91
MPC		0.51
ClinPred		0.98	D
GERP RS		5.5
Varity_R		0.51
gMVP		0.61

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.0		Details are displayed if max score is > 0.2

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Publications

LitVar

Other links and lift over

dbSNP: rs187379039; hg19: chr15-91306286;